Water treatment system and methods thereof

ABSTRACT

A water treatment system with a photocatalytic nanocomposite sheet, an adsorbent layer, and a fibrous filter, wherein the photocatalytic nanocomposite sheet comprises polymethylmethacrylate and silver phosphate, the adsorbent layer comprises plasma activated carbon nanotubes, and the fibrous filter is a composite of polymethylmethacrylate, polyvinylidene fluoride, and polyvinylpyrrolidone polymer fibers, with carbon nanotubes that are dispersed within the polymer fibers and silver nanoparticles that are deposited on the polymer fibers. Various embodiments of the water treatment system and methods of fabricating the photocatalytic nanocomposite sheet, the adsorbent layer, and the fibrous filter are also provided.

BACKGROUND OF THE INVENTION Technical Field

The present invention relates to a water treatment system that includesa photocatalytic nanocomposite sheet, an adsorbent layer, and a fibrousfilter, and methods of fabricating thereof.

Description of the Related Art

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admitted as prior art against the presentinvention.

Water pollution is a major concern for industrial areas and urban cites.Organic pollutants originated from petrochemical and manufacturingindustry can cause serious environmental hazards. Various physical,chemical, and biological methods have been developed to effectivelyremove organic pollutants from wastewater [Numan Salah, A. Hameed, M.Aslam, M. Sh. Abdel-wahab, Saeed S. Babkair, F. S. Bahabri, Flowcontrolled fabrication of N doped ZnO thin films and estimation of theirperformance for sunlight photocatalytic decontamination of water,Chemical Engineering Journal 291 (2016)115; F. Hodin, H. Borén, A.Grimvall, Water Sci. Technol. 24 (1991) 403; N. Wang, X. Li, Y. Wang, X.Quan, G. Chen, Chemical Engineering Journal, 146, (2009) 30]. However,such materials and methods are very costly. One example is advancedoxidation processes (AOPs) for removing toxic chemical pollutants fromwastewater. Among various AOPs recognized, the photocatalysis approachis a well-known approach, whereby organic pollutants are converted toCO₂ in the presence of a catalyst, e.g. zinc oxide (ZnO) [Numan Salah,A. Hameed, M. Aslam, M. Sh. Abdel-wahab, Saeed S. Babkair, F. S.Bahabri, Flow controlled fabrication of N doped ZnO thin films andestimation of their performance for sunlight photocatalyticdecontamination of water, Chemical Engineering Journal 291 (2016)115; M.Tariq Qamar, M. Aslam, Iqbal M. I. Ismail, Numan Salah, A. Hameed, Theassessment of the photocatalytic activity of magnetically retrievableZnO coated γ-Fe₂O₃ in sunlight exposure, Chemical Engineering Journal,283, (2016) 656] or titanium dioxide (TiO₂) [S. G. Rashid, M. A. Gondal,A. Hameed, M. Aslam, M. A. Dastageer, Z. H. Yamani, D. H. Anjum,Synthesis, characterization and visible light photocatalytic activity ofCr³⁺, Ce³⁺ and N co-doped TiO₂ for the degradation of humic acid, RSCAdv., 5, (2015) 32323]. However, producing these catalysts in largequantities is very costly. On the other hand, the time needed forpollutant degradation is relatively long. Therefore, it is important tofind a high performance and inexpensive materials for a fast degradationof organic pollutants.

Extensive research work has recently been conducted on the design of avisible-light photocatalytic material for degradation of organicpollutants. Silver phosphate (Ag₃PO₄) has been considered as avisible-light photocatalyst and as a replacement for other knownphotocatalyst materials such as TiO₂ and ZnO. Silver phosphate revealeda quantum efficiency of up to 90% at wavelengths above 420 nm. Silverphosphate was also found to be a strong photo-oxidant. [Chao Dong,Kong-LinWu, Meng-Ran Li, Li Liu, Xian-Wen Wei, Synthesis of Ag₃PO₄—ZnOnanorod composites with high visible-light photocatalytic activity,Catalysis Communications 46, (2014) 32; Yingpu Bi, Hongyan Hu, ShuxinOuyang, Gongxuan Lu, Junyu Cao and Jinhua Ye, Photocatalytic andphotoelectric properties of cubic Ag₃PO₄ sub-microcrystals with sharpcorners and edges, hem. Commun., 48, (2012) 3748; I. S. Yahia, AsimJilani, Mohamed S. Hlamdy, M. Sh. Abdel-wahab, H. Y. Zahran, M.Shahnawaze Ansari, Attieh A. Al-Ghamdi, The photocatalytic activity ofgraphene oxide/Ag₃PO₄ nano-composite: Loading effect, Optik, 127, (2016)10746; Zheng-Mei Yang, Gui-Fang Huang, Wei-Qing Huang, Jia-Mou Wei,Xin-Guo Yan, Yue-Yang Liu, Chao Jiao, Zhuo Wan and Anlian Pan, NovelAg₃PO₄/CeO₂ composite with high efficiency and stability forphotocatalytic applications, J. Mater. Chem. A, 2, (2014) 1750]. Anumber of research articles reported that Ag₃PO₄ has a highphotocatalytic efficiency due to the high rate of electron/holeseparation [Yunfang Wang, Xiuli Li, Yawen Wang, Caimei Fan, Novelvisible-light AgBr/Ag₃PO₄ hybrids photocatalysts with surface plasmaresonance effects, Journal of Solid State Chemistry, 202, (2013) 51].However, using catalysts in a powder form is challenging, due toagglomeration of catalyst particles and the difficulty of removing thecatalyst particles after a treatment process.

Electrospun polyvinylidene fluoride (PVDF) nanofibers are widely used inwater filtration systems because of a good oxidation stability, a goodthermal stability, and a good hydrolytic stability of the PVDFnanofibers. However, the relatively low mechanical stability andnon-uniform pores distribution of the PVDF nanofibers largely restrictthe applications of nanofibers [Z. Ma, M. Kotaki, S. Ramakrishna,Electrospun cellulose nanofiber as affinity membrane, J. Membr. Sci.,265, (2005) 115]. To overcome this drawback, several research studieshave investigated the stability of the PVDF nanofiber afterincorporating nanomaterials such as TiO₂ [J. H. Li, Y. Y. Xu, L. P. Zhu,J. H. Wang, C. H. Du, Fabrication and characterization of novel TiO₂nanoparticle self-assembly membrane with improved fouling resistance, J.Membr. Sci., 326, (2009) 659], Al₂O₃[Y. Lu, S. L. Yu, B. X. Chai,Preparation of poly (vinylidene fluoride) ultrafiltration membranemodified by nano-sized alumina (Al₂O₃) and its antifouling research,Polymer, 46, (2005) 7701], silver nanoparticles [L. Francis, F. Giunco,A. Balakrishnan, E. Marsano, Synthesis, characterization and mechanicalproperties of nylon-silver composite nanofibers prepared byelectrospinning, Curr. Appl. Phys., 10, (2010) 1005], and carbonnanotubes [S. Aryal, C. K. Kim, K. W. Kim, M. S. Khil, H. Y. Kim,Multi-walled carbon nanotubes/TiO₂ composite nanofiber byelectrospinning, Mater. Sci. Eng. C, 28, (2008) 75]. It was shown thatincorporating the aforementioned nanomaterials in the PVDF nanofibersenhanced the mechanical properties, thermal and chemical stability,separation performance, etc. of the PVDF nanofibers.

Several reports focused on designing and developing variety of compositematerials for water treatments. For example, Berge et al. [J. Berge, JBoutillier, P. Delprat., Patent no. FR2948036B1], reported on the use ofa transparent composition based on methacrylic polymers for theconstruction of a photo-reactor in the field of treatment of drinkingwater, waste water pollution control, treatment of air or gas,deodorizing or decontamination of soil. Cheng et al. [S. Cheng, X. Li.,Ag₃PO₄ photo-catalysis coupling constructed wetland microorganism fuelbattery system and its application, Patent no. CN 105859024A] reported acathode conductive material layer filled with a conductive carbonmaterial and a photocatalyst Ag₃PO₄ for fuel battery system. Tarifi etal. [Mohamed H. Tarifi. Pco/uvc/carbon water filter, US patentapplication no. US20140166591A1] developed a water treatment system thatcontains activated carbon and titanium dioxide as a photocatalyticfilter with the use of ultraviolet lamp. Chen et al. [G. Chen, M. Sun,Q. Wei, Y. Zhang, B. Zhu, B Du, Ag₃PO₄/graphene-oxide composite withremarkably enhanced visible-light-driven photocatalytic activity towarddyes in water, Journal of Hazardous Materials, 244-245, (2013) 86-93]produced Ag₃PO₄/graphene-oxide composite for the removal of dyes inwater. Similarly Dong et al. [P. Dong, Y. Wang, B. Cao, S. Xin, L. Guo,J. Zhang, F. Li, Ag₃PO₄/reduced graphite oxide sheets nanocompositeswith highly enhanced visible light photocatalytic activity andstability, Applied Catalysis B: Environmental, 132-133, (2013) 45-53]synthesized Ag₃PO₄/reduced graphite oxide nanocomposites and Bai et al.[S. Bai, X. Shen, H. Lv, G. Zhu, C. Bao, Y. Shan, Assembly of Ag₃PO₄nanocrystals on graphene-based nanosheets with enhanced photocatalyticperformance, Journal of Colloid and Interface Science, 405, (2013) 1-9]produced Ag₃PO₄/Graphene nanocomposites. Xu et al. [L. Xu, Y. Wang, J.Liu, S. Han, Z. Pan, Lu Gan, High-efficient visible-light photocatalystbased on grapheme incorporated Ag₃PO₄ nanocomposite applicable for thedegradation of a wide variety of dyes, Journal of Photochemistry andPhotobiology A: Chemistry, Accepted Manuscript 2017, DOI:http://dx.doi.org/doi: 10.1016/j.jphotochem.2017.02.022] synthesized ananocomposite of Ag₃PO₄ and graphene in a powder form for thedegradation of a wide variety of dyes. Jiang et al. [D. Jiang, J. Zhu,M. Chen, J. Xie, Highly efficient heterojunction photocatalyst based onnanoporous g-C₃N₄ sheets modified by Ag₃PO₄ nanoparticles: Synthesis andenhanced photocatalytic activity, Journal of Colloid and InterfaceScience, 417, (2014) 115-120] fabricated a heterojunction photocatalystbased on nanoporous g-C₃N₄ sheets modified by Ag₃PO₄ nanoparticles. Qinet al. [L. Qin, P. Tao, X. Zhou, X. Luo, Synthesis and characterizationof high efficiency and stable spherical Ag₃PO₄ visible lightphotocatalyst for the degradation of methylene blue solutions, Journalof Nanomaterials, (2015) Article ID 258342] synthesized spherical Ag₃PO₄for the degradation of methylene blue solutions. Hui et al. [X. Hui, C.Wang, Y. Song, H. Li, CNT/Ag₃PO₄ composites with highly enhanced visiblelight photocatalytic activity and stability, Chemical EngineeringJournal, 241, (2014) 35-42] reported the synthesis of a heterojunctionstructure of CNT/Ag₃PO₄ composite. Similarly, Liu et al. [B. Liu, Z. Li,S. Xu, D. Han, D. Lu, Enhanced visible-light photocatalytic activitiesof Ag₃PO₄/MWCNT nanocomposites fabricated by facile in situprecipitation method, Journal of Alloys and Compounds, 596, (2014)19-24] produced Ag₃PO₄/MWCNT powder nanocomposites by a facile in-situprecipitation method. Wang et al. [S. Wang, S. Liang, P. Liang, X.Zhang, J. Sun, S. Wu, X. Huang, In-situ combined dual-layer CNT/PVDFmembrane for electrically-enhanced fouling resistance, Membrane Science,491, (2015) 37-44] fabricated a CNT/PVDF membrane forelectrically-enhanced fouling resistance.

In view of the forgoing, one objective of the present invention is toprovide a water treatment system that includes a photocatalyticnanocomposite sheet. The sheet is a composite of polymethylmethacrylateand silver phosphate, which is located inside a transparent section of apipe or vessel in the water treatment system. The water treatment systemfurther includes an adsorbent layer of plasma activated carbonnanotubes, and a fibrous filter that is a composite ofpolymethylmethacrylate, polyvinylidene fluoride, andpolyvinylpyrrolidone polymer fibers, with carbon nanotubes that aredispersed within the polymer fibers and silver nanoparticles that aredeposited on the polymer fibers. Another objective of the presentinvention relates to methods of fabricating the photocatalyticnanocomposite sheet, the adsorbent layer, and the fibrous filter.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect, the present disclosure relates to a watertreatment system, including i) a pipe comprising a water inlet, a wateroutlet, and a transparent section located between the water inlet andthe water outlet, ii) a photocatalytic nanocomposite sheet comprisingpolymethylmethacrylate and silver phosphate located inside thetransparent section, wherein the photocatalytic nanocomposite sheet isconfigured to decompose at least a portion of organic pollutants presentin water.

In one embodiment, the transparent section is coil shaped.

In one embodiment, the photocatalytic nanocomposite sheet has athickness in the range of 0.5 to 2 mm.

In one embodiment, the water treatment system further includes at leastone mirror configured to reflect sunlight to the transparent section.

In one embodiment, the water treatment system further includes i) afilter housing with an inlet and an outlet, ii) a fibrous filter locatedinside the filter housing and between the inlet and the outlet, whereinthe inlet is fluidly connected to the water outlet.

In one embodiment, the fibrous filter includes polymer fibers comprisingpolymethylmethacrylate, polyvinylidene fluoride, andpolyvinylpyrrolidone, and silver nanoparticles deposited on the polymerfibers.

In one embodiment, the fibrous filter has pores with an average poresize in the range of 5 to 50 nm.

In one embodiment, the fibrous filter further includes carbon nanotubesthat are dispersed in the polymer fibers.

In one embodiment, the water treatment system further comprises anadsorbent layer of plasma activated carbon nanotubes located within thefilter housing between the fibrous filter and the inlet.

According to a second aspect, the present disclosure relates to a methodof purifying water with the water treatment system, involving passingthe water through the photocatalytic nanocomposite sheet to formpurified water.

In one embodiment, the water treatment system further includes thefilter housing and the fibrous filter, and the method involves passingthe water through the photocatalytic nanocomposite sheet and the fibrousfilter to form purified water.

In one embodiment, a ratio of a total organic carbon content of thewater to a total organic carbon content of the purified water is in therange of 2:1 to 5:1.

According to a third aspect, the present disclosure relates to a methodof fabricating the photocatalytic nanocomposite sheet, involving i)mixing silver phosphate nanoparticles with a polymer solution comprisingpolymethylmethacrylate in an organic solvent to form a suspension, ii)sonicating the suspension, iii) casting the suspension on a substrate toevaporate the organic solvent and form the photocatalytic nanocompositesheet.

In one embodiment, the organic solvent is chloroform, and the polymersolution is formed by dissolving polymethylmethacrylate in chloroform ata temperature of 35 to 55° C.

According to a fourth aspect, the present disclosure relates to a methodof fabricating the fibrous filter, involving i) mixing a colloidalsuspension comprising silver nanoparticles, polyvinylpyrrolidone, anddimethylformamide with a ketone-based solvent to form a precursorsuspension, ii) mixing polyvinylidene fluoride with the precursorsuspension to form a first suspension, iii) separately mixingpolymethylmethacrylate with the precursor suspension to form a secondsuspension, iv) mixing the first suspension with the second suspensionto form an electrospin suspension, v) electrospinning the electrospinsuspension to form the fibrous filter, wherein the fibrous filtercomprises polymer fibers comprising polymethylmethacrylate,polyvinylidene fluoride, and polyvinylpyrrolidone, and silvernanoparticles deposited on the polymer fibers.

In one embodiment, the ketone-based solvent is acetone, and thecolloidal suspension is mixed with acetone at a volume ratio of 3:1 to5:1.

In one embodiment, a weight percent of polyvinylidene fluoride in thefirst suspension is 10 to 20 wt % relative to the total weight of thefirst suspension, and a weight percent of polymethylmethacrylate in thesecond suspension is 10 to 20 wt % relative to the total weight of thesecond suspension.

In one embodiment, the first suspension is mixed with the secondsuspension at a volume ratio of 2:1 to 4:1.

In one embodiment, the method further includes mixing a carbon nanotubesuspension comprising carbon nanotubes and dimethylformamide with theelectrospin suspension and sonicating prior to the electrospinning.

In one embodiment, the carbon nanotube suspension has a carbon nanotubeconcentration of 0.5 to 2 g/L, and the carbon nanotube suspension ismixed with the electrospin suspension at a volume ratio of 1:6 to 1:10.

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. The described embodiments, together with further advantages,will be best understood by reference to the following detaileddescription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1A shows the water purification system of this disclosure thatincludes a photocatalytic nanocomposite sheet, an adsorbent layer, and afibrous filter.

FIG. 1B shows the adsorbent layer and the fibrous filter in the filterhousing.

FIG. 1C shows the photocatalytic nanocomposite sheet that is placed in aU-shape glass tube.

FIG. 1D shows the photocatalytic nanocomposite sheet that is inserted ina U-shape glass tube.

FIG. 2A is an optical image of the photocatalytic nanocomposite sheet.

FIG. 2B is a magnified optical image of the photocatalytic nanocompositesheet. Silver phosphate particles are observed in the form ofnanocrystals.

FIG. 3 is a SEM image of the fibrous filter.

FIG. 4 is a TEM image of a polymer fiber in the fibrous filter.

FIG. 5 is an optical image of a contact angle of a water droplet and thefibrous filter.

FIG. 6 shows contaminated water samples before and after treatment withthe water treatment system.

FIG. 7 represents UV/Vis absorption spectra of a contaminated watersample having methylene blue, a) before any treatment, b) aftertreatment with only the photocatalytic nanocomposite sheet, c) aftertreatment with the photocatalytic nanocomposite sheet, the adsorbentlayer, and the fibrous filter.

FIG. 8 represents HPLC profiles of a contaminated water sample havingmethylene blue, a) before any treatment, b) after treatment with onlythe photocatalytic nanocomposite sheet, c) after treatment with thephotocatalytic nanocomposite sheet, the adsorbent layer, and the fibrousfilter.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views.

According to a first aspect, the present disclosure relates to a watertreatment system 100, including a pipe 104 that has a water inlet 101, awater outlet 107, and a transparent section 102 located between thewater inlet 101 and the water outlet 107.

The term “pipe” refers to a means for carrying a fluid or a liquidstream, e.g. a water stream. The pipe 104 may have a circular,rectangular, triangular, elliptical, or rectilinear cross-section.Preferably, the pipe has a circular cross-section with a diameter in therange of 10 to 100 mm, preferably 20 to 90 mm, preferably 30 to 80 mm,preferably 40 to 60 mm, preferably about 50 mm. The pipe may have auniform cross-section, wherein a cross-sectional area is substantiallythe same along the length of the pipe, or may have a non-uniformcross-section, wherein a cross-sectional area is not the same along thelength of the pipe. However, a cross-sectional area of the pipe alongthe transparent section is preferably substantially the same.

The length of the pipe 104 may vary from about 0.5 m to about 50 m,preferably from about 1.0 m to about 30 m, preferably from about 2 m toabout 20 m, preferably from about 3 m to about 20 m, preferably fromabout 4 m to about 15 m, preferably from about 5 m to about 10 m.Accordingly, the length of the transparent section may preferably be atleast 50%, preferably at least 60%, preferably at least 70%, preferablyat least 80%, preferably at least 90% of the total length of the pipe.Accordingly, in one embodiment, the transparent section 102 has a totalvolume capacity in the range of 1 to 50 L, preferably 2 to 45 L,preferably 5 to 40 L, preferably 10 to 35 L, preferably 15 to 30 L,preferably about 20 L.

The term “transparent section” of the pipe refers to a section of thepipe that is transparent and thus allows sunlight, more particularlytransparent to infrared, visible light, and/or ultra violet radiation,to pass through. In a preferred embodiment, the transparent section 102is in the form of a coil (as shown in FIG. 1A) to provide an extendedsurface area to solar radiation. In one embodiment, the transparentsection 102 is made of a plurality of U-shape tubes 103 (as shown inFIGS. 1C and 1D) that are coupled together to form the coil.Accordingly, the transparent section may be made of at least 3,preferably at least 5, preferably at least 10, preferably at least 15,preferably at least 20, preferably at least 25, preferably at least 30,preferably at least 35, preferably at least 40, but no more than 100 ofthe U-shape tubes 103 that are coupled together. In one embodiment, anexternal surface area of the transparent section is sufficient toreceive a light illuminance of at least 100,000 lux, preferably at least110,000 lux, more preferably at least 120,000 lux, but no more than200,000 lux.

In one embodiment, the transparent section is made of a transparentmaterial. Exemplary transparent materials include, but are not limitedto glass, general purpose polystyrene (GPPS), polycarbonate (PC), polymethylmethacrylate (PMMA), styrene acrylonitrile (SAN), styrene methylmethacrylate (SMMA), polyethylene terephthalate glycol-modified (PET-G),methyl methacrylate butadiene styrene (MBS), and/or any combinationthereof. In a preferred embodiment, the transparent section is made ofquartz.

In another preferred embodiment, the water treatment system 100 furtherincludes one or more mirrors 120 located in the vicinity of thetransparent section 102 of the pipe 104. Said mirrors are configured toreflect sunlight to the transparent section (as shown in FIG. 1A).

The term “in the vicinity of the transparent section” as used hereinrefers to a location within a distance no more than 100 cm, preferablyno more than 90 cm, preferably no more than 80 cm, preferably no morethan 70 cm, preferably no more than 60 cm, preferably no more than 50cm, from the transparent section.

In one embodiment, said mirrors 120 are located underneath and parallelto the transparent section, wherein a gap of about 10 to 50 cm,preferably 20 to 40 cm is present between said mirrors and thetransparent section. Preferably, the mirror is located underneath theentire length of the transparent section.

In a preferred embodiment, said mirrors 120 are concave mirrors to focussolar radiation to a focal point. Accordingly, the transparent sectionis located with respect to the focal point such that the transparentsection falls at the focal point.

The water treatment system 100 may optionally include a pump or suctionsource 118 to flow a water stream within the pipe, or to adjust the flowrate of the water stream within the pipe. The pump 118 may be acentrifugal, a rotatory, or a positive displacement pump; although thetype of pump used is not meant to be limiting and other types of pumpsmay also be used. In addition to the pump, a flow-rate control systemmay also be utilized to regulate the flow rate of the water streamthrough the pipe and, particularly through the transparent section ofthe pipe. The flow-rate control system may include a flow meter todetermine a flow rate within the pipe and/or within the transparentsection, a processing unit in communication with the flow meter toreceive an input signal and transmit an output signal to an actuator tooperate a valve to adjust the flow rate of the water stream within thepipe and/or within the transparent section. In another embodiment, adetector is utilized to instantaneously measure a total organic carboncontent of a water stream that outflows the transparent section.Accordingly, the detector is in communication with the processing unitand the actuator via a feedback control system. Said control system isconfigured to adjust the flow rate of the water stream within the pipeand/or within the transparent section, based on variations of the totalorganic carbon content in the water stream.

The water treatment system 100 further includes a photocatalyticnanocomposite sheet 105 that is located inside the transparent section102 of the pipe 104.

The term “photocatalytic nanocomposite sheet” as used in this disclosurerefers to a composite of polymethylmethacrylate (PMMA) and silverphosphate (Ag₃PO₄) nanoparticles that is in a form of a sheet with athickness in the range of 0.5 to 2 mm, preferably 0.6 to 1.8 mm,preferably 0.7 to 1.5 mm, preferably 0.8 to 1.2 mm, more preferablyabout 1 mm. Said photocatalytic nanocomposite sheet is configured todecompose at least a portion of organic pollutants present in water,when exposed to direct sunlight. In a preferred embodiment, a weightratio of silver phosphate (Ag₃PO₄) to polymethylmethacrylate (PMMA)ranges between 1:15 to 1:40, preferably 1:18 to 1:30, more preferablyabout 1:20. In another embodiment, a weight percent of silver phosphate(Ag₃PO₄) in the photocatalytic nanocomposite sheet is in the range of 2to 8 wt %, preferably 3 to 6 wt %, preferably about 4.5 wt %, relativeto the total weight of the photocatalytic nanocomposite sheet.Accordingly, a weight percent of polymethylmethacrylate (PMMA) in thephotocatalytic nanocomposite sheet is in the range of 90 to 98 wt %,preferably 93 to 97 wt %, preferably about 95 wt %, relative to thetotal weight of the photocatalytic nanocomposite sheet. In addition, thephotocatalytic nanocomposite sheet may have a specific surface area inthe range of 5 to 50 m²/g, preferably 10 to 40 m²/g, preferably 12 to 30m²/g, preferably 15 to 20 m²/g.

Accordingly, the transparent section of the water treatment system isplaced in an uncovered location under solar radiation, wherein a lightilluminance received by the photocatalytic nanocomposite sheet in thetransparent section is in the range of 5,000 to 120,000 lux, preferably10,000 to 110,000 lux, more preferably 30,000 to 100,000 lux, even morepreferably 50,000 to 80,000 lux. In another embodiment, a lightirradiance received by the photocatalytic nanocomposite sheet in thetransparent section may preferably be in the range of 200-1,200 W/m²,preferably 250-1,000 W/m², more preferably 300-850 W/m². An opticalmicrograph of the photocatalytic nanocomposite sheet 105 is shown inFIGS. 2A and 2B.

In the absence of solar radiation, for example, in a cloudy day or atnights, the transparent section of the water treatment system may beexposed to an artificial light source, wherein a light irradiancereceived by the photocatalytic nanocomposite sheet in the transparentsection may be in the range of 100-1,000 W/m², preferably 150-800 W/m²,more preferably 200-500 W/m². Exemplary artificial light sourcesinclude, but are not limited to a microwave, a UV light, a visible lightbulb, a fluorescent bulb/tube, an X-ray source, a γ-ray source, and aninfrared source.

One aspect of the invention relates to a method of fabricating thephotocatalytic nanocomposite sheet 105. The method involves mixingsilver phosphate nanoparticles with a polymer solution to form asuspension. The silver phosphate nanoparticles may have an average sizein the range of 10 to 80 nm, preferably about 20 to 70 nm, preferablyabout 30 to 60 nm, preferably about 40 to 50 nm.

In one embodiment, the polymer solution includes polymethylmethacrylatedissolved in an organic solvent. A concentration ofpolymethylmethacrylate in the polymer solution is preferably in therange of 10 to 30 g/L, preferably 15 to 25 g/L, preferably about 20 g/L.For example, in one embodiment, 1 to 3 g, preferably 1.5 to 2.5 g,preferably about 2 g of PMMA is dissolved in 100 mL of an organicsolvent. In addition a weight ratio of the silver phosphatenanoparticles to that of PMMA in the suspension is in the range of 1:10to 1:30, preferably 1:15 to 1:25, preferably about 1:20. For example, inone embodiment, the suspension includes about 80 to 120 mg, preferablyabout 100 mg of the silver phosphate nanoparticles, and about 1.8 to 2.2g, preferably about 2 g of PMMA in about 80 to 120 mL, preferably about100 mL of an organic solvent.

The organic solvent may be one or more solvent selected from the groupconsisting of methanol, toluene, tetrahydrofuran, acetic acid, acetone,acetonitrile, butanol, dichloromethane, chlorobenzene, dichloroethane,diethylene glycol, diethyl ether, dimethoxy-ethane, dimethyl-formamide,dimethyl sulfoxide, ethanol, ethyl acetate, ethylene glycol, heptane,methyl t-butyl ether, methylene chloride, pentane, cyclopentane, hexane,cyclohexane, benzene, dioxane, propanol, isopropyl alcohol, pyridine,triethyl amine, propandiol-1,2-carbonate, ethylene carbonate, propylenecarbonate, nitrobenzene, formamide, benzyl alcohol,n-methyl-2-pyrrolidone, acetophenone, benzonitrile, dimethyl sulfate,aniline, phenol, dichlorobenzene, tri-n-butyl phosphate, ethylenesulfate, benzenethiol, dimethyl acetamide, cyclohexanol, bromobenzene,cyclohexanone, 1-hexanethiol, ethyl chloroacetate, 1-dodecanthiol,di-n-butylether, dibutyl ether, acetic anhydride, m-xylene, o-xylene,and p-xylene. Depending on the type of solvent used, the polymersolution is formed by dissolving polymethylmethacrylate in the organicsolvent at a temperature that is at least 10° C., preferably 15 to 20°C. above room temperature (i.e. 25° C.) and 5 to 15° C., preferablyabout 10° C. below the boiling point of the organic solvent. Forexample, in a preferred embodiment, the organic solvent is chloroform,and the polymer solution is formed by dissolving polymethylmethacrylatein chloroform at a temperature of 35 to 60° C., preferably 45 to 55° C.,more preferably about 50° C.

After mixing the silver phosphate nanoparticles with the polymersolution, the suspension is sonicated at room temperature (i.e. 25° C.),and preferably stirred concurrently during sonication until a yellowsuspension is obtained.

After sonicating the suspension, the suspension is casted on asubstrate, e.g. a petri dish, to evaporate at least a portion of theorganic solvent and form the photocatalytic nanocomposite sheet.Preferably the suspension is kept for a sufficient time, e.g. 24 hours,preferably 48 hours, on the substrate in an elevated temperature, 35 to60° C., preferably 45 to 55° C., more preferably about 50° C., toentirely evaporate the organic solvent. The substrate may be a glasssubstrate, preferably a flexible rubber substrate, e.g. silicon rubber,that allows an easy removing of the photocatalytic nanocomposite sheetfrom the substrate.

Preferably, the photocatalytic nanocomposite sheet 105 is secured insidethe transparent section 102 of the pipe 104 such that the photocatalyticnanocomposite sheet 105 covers at least a portion of an internal surfacearea of the transparent section of the pipe 104 (as shown in FIGS. 1Cand 1D). Placing the photocatalytic nanocomposite sheet inside thetransparent section of the pipe can be done by, for example, rolling thephotocatalytic nanocomposite sheet to form a tube shape, and insertingsaid tube-shaped photocatalytic sheet into individual U-shape tubes thatare separated from each other, and further coupling said U-shape tubesto form the transparent section.

The photocatalytic nanocomposite sheet 105 is configured to decompose atleast a portion of organic pollutants present in water in the presenceof sunlight.

In a preferred embodiment, the water treatment system 100 furtherincludes a filter housing 108 and a fibrous filter 110 located therein.The term “filter housing” as used herein refers to a container with aninlet 114 and an outlet 116, and an internal cavity that is configuredto hold a liquid preferably at elevated pressures, for example, apressure in the range of 0.5-10 bars, preferably 1-5 bars. The filterhousing 108 may be made of alumina, quartz, stainless steel, nickelsteel, chromium steel, aluminum, aluminum alloy, copper and copperalloys, titanium, and the like, although the materials used to constructthe filter housing are not meant to be limiting and various othermaterials may also be used. In one embodiment, a portion of an internalsurface of the filter housing is coated with a polymeric lining tominimize surface oxidation. The polymeric lining may be an epoxy or avinyl ester, preferably a BPA-free polymer such as polyethylene,polypropylene, or polytetrafluoroethylene. In one embodiment, the filterhousing has an internal volume in the range of 0.1-1,000 L, preferably5-500 L, or preferably 10-150 L, or preferably 50-100 L. Geometry of thefilter housing may be one of cylindrical, cubic, rectangular, spherical,oblong, conical, or pyramidal. Preferably, the filter housing iscylindrical and is vertically oriented (as shown in FIGS. 1A and 1B).The filter housing may also be a cylindrical container that ishorizontally oriented. In another preferred embodiment, the filterhousing is portable having an internal volume in the range of 0.5-10.0L, preferably 1-8.0 L, more preferably 2-5.0 L.

The inlet 114 and the outlet 116 are utilized as passages for loadingand unloading the filter housing 108 with water. In one embodiment, theinlet 114 and the outlet 116 are substantially the same, wherein each isa cylindrical port having an internal diameter in the range of 1-20 mm,preferably 5-10 mm. The inlet 114 and the outlet 116 are configured topass water with a flow rate of up to 500 L/min, preferably up to 1,000L/min. The inlet 114 and the outlet 116 may be secured with threadedfittings, or other means, to the filter housing 108.

In one embodiment, the filter housing is a vertically oriented cylinderthat includes a liquid distributor located inside the filter housing andattached to the inlet 114. The liquid distributor is configured todivide an inlet stream that enters the filter housing into a pluralityof streams and distributes said streams throughout a cross-section ofthe filter housing. The liquid distributor may be made of glass ormetal, and can be used in any shape, preferably disc shape, cylindrical,or spherical. For example, in one embodiment, the liquid distributor hasa perforated disc-shape structure. Size of perforations in the liquiddistributor may be different ranging from 0.5-2 mm, preferably about 1mm.

Preferably, the inlet 114 and the outlet 116 are located on oppositeends (as shown in FIG. 1B), although in some embodiments, the inlet andthe outlet may be located on the same end.

In one embodiment, the inlet 114 and the outlet 116 are located onopposite ends, and the fibrous filter 110 is located inside the filterhousing and between the inlet and the outlet. The inlet 114 of thefilter housing is fluidly connected to the water outlet 107 of the pipe.

In some embodiments, the fibrous filter 110 includes polymer fibers ofpolymethylmethacrylate (PMMA), polyvinylidene fluoride (PVDF), andpolyvinylpyrrolidone (PVP). In addition, silver nanoparticles aredeposited on the polymer fibers. In one embodiment, a weight percent ofsilver nanoparticles that are deposited on the polymer fibers is in therange of 0.5 to 5 wt %, preferably 1 to 3 wt %, more preferably about 1to 1.5 wt %, relative to the total weight of the fibrous filter.Additionally, a weight ratio of polymethylmethacrylate (PMMA) topolyvinylidene fluoride (PVDF) may be in the range of 1:1 to 1:2,preferably about 1:1, whereas a weight ratio of polymethylmethacrylate(PMMA) to polyvinylpyrrolidone (PVP) may be in the range of 1:1 to 1:2,preferably about 1:1.5.

The term “fibrous filter” as used herein refers to a filter that is madeof polymer fibers, preferably interwoven polymer fibers. The diameter ofeach fiber ranges from about 20 nm to about 2 μm, preferably from about50 nm to about 1 m, preferably from about 100 nm to about 500 nm.Accordingly, the fibrous filter is a porous polymer structure havingpores with an average pore size in the range of 5 to 50 nm, preferably10 to 45 nm, preferably 15 to 40 nm. The silver nanoparticles that aredeposited on the polymer fibers (as shown in FIG. 4) may have a sizerange of 1 to 100 nm, preferably 5 to 90 nm, preferably 10 to 80 nm. Inone embodiment, the silver nanoparticles are configured to preventformation of and/or kill microorganisms (e.g. bacteria) present withinthe fibrous filter or contaminated water, and thus the silvernanoparticles may provide an anti-biofouling property to the fibrousfilter.

In one embodiment, the fibrous filter 110 further includes carbonnanotubes that are dispersed in the polymer fibers to provide mechanicalstability to the fibrous filter. Accordingly, a weight percent of carbonnanotubes present in the fibrous filter is in the range of 0.5 to 5 wt%, preferably 1 to 4 wt %, preferably 1.5 to 3.5 wt %, preferably about2 wt %, relative to the total weight of the fibrous filter.

In one embodiment, the term “mechanical stability” as used herein refersto an enhancement in flexural modulus by at least 20%, preferably atleast 50%, more preferably at least 80%, even more preferably at least100%, relative to a flexural modulus of a fibrous filter without havingcarbon nanotubes. For example, in one embodiment, a flexural modulus ofthe fibrous filter without having the carbon nanotube is in the range of50 to 500 kPa, whereas a flexural modulus of the fibrous filter with thecarbon nanotube is in the range of 100 kPa to 1 MPa. The term“mechanical stability” may also refer to an enhancement in fracturetoughness, flexural strength, and tear strength.

Preferably, the carbon nanotubes are multi-walled carbon nanotubes(MWCNT) with a diameter in the range of 5-20 nm, preferably 8-15 nm,more preferably about 10 nm, and an aspect ratio of greater than orequal to about 5, preferably greater than or equal to about 100, morepreferably greater than or equal to about 1000. The multi-walled carbonnanotubes may be closed structures having hemispherical caps at each endof respective tubes, or they may have a single open end or both openends. Alternatively, the carbon nanotubes may be single-walled carbonnanotubes (SWCNT) with a diameter within the range of 0.5-3 nm,preferably 1-2 nm, more preferably about 1.5 nm, and an aspect ratio ofgreater than or equal to about 50, preferably greater than or equal toabout 100, more preferably greater than or equal to about 1000. Thesingle-walled carbon nanotubes may be closed structures havinghemispherical caps at each end of respective tubes, or they may have asingle open end or both open ends.

In one embodiment, the carbon nanotubes as used in this disclosure areproduced from fly ash using chemical vapor deposition as reported bySalah et al. [U.S. Pat. No. 8,609,189 B2; incorporated by reference inits entirety].

Alternative means to provide mechanical stability to the fibrous filtermay also be adopted herein. For example, in one embodiment, a doublelayered mesh structure is utilized, wherein the fibrous filter isdisposed between the two layers of the double layered mesh structure.Said mesh structure is configured to secure the fibrous filter in placewithin the filter housing and provide flexural strength to the fibrousfilter, while allowing a water stream to pass through the fibrousfilter. Said mesh structure may have a mesh size of less than 5 mm,preferably less than 2 mm. The term “mesh size” as used herein refers tothe size of the holes (i.e. meshes) present in said mesh structure, asmeasured via ASTM E11:01.

In one embodiment, the water treatment system further includes anadsorbent layer 112 located within the filter housing 108, wherein theadsorbent layer comprises plasma activated carbon nanotubes to adsorb atleast a portion of the organic pollutants present in water. Theadsorbent layer 112 may preferably be located between the fibrous filter110 and the inlet 114 of the filter housing 108, although the adsorbentlayer 112 can also be located between the fibrous filter 110 and theoutlet 116 of the filter housing 108.

In some embodiments, the adsorbent layer 112 is formed by plasmatreatment of carbon nanotubes in an oxygen atmosphere. Accordingly, aceramic crucible, which contains carbon nanotubes, is placed in achamber of a microwave chemical vapor deposition system. The chamber isevacuated to a pressure of about 10⁻³ Pa, preferably about 10⁻⁴ Pa. Thechamber is then purged with oxygen. Then, plasma activation starts afterthe chamber is filled with oxygen. Preferably, the plasma activation iscontinued for a period of about 5 to 120 minutes, preferably about 20 to50 minutes, preferably 25 to 35 minutes, more preferably about 30minutes, under a power of about 300 to 600 Watt, preferably about 500Watt. In one embodiment, a specific surface area of carbon nanotubesincreased by at least 5%, preferably at least 10%, preferably at least15%, preferably at least 20%, preferably at least 25%, preferably atleast 30%, relative to the specific surface area of carbon nanotubesprior to the plasma treatment. In another embodiment, the carbonnanotubes are surface functionalized with one or more functional groupsselected from C—O, C═O, and O—C═O.

The plasma activated carbon nanotubes may be in the form of abuckypaper. The term “buckypaper” as used herein refers to a film-shapedaggregate of plasma activated carbon nanotubes. Having the plasmaactivated carbon nanotubes in the form of a buckypaper may enhance aneffective electroactive surface area through which organic pollutantsare adsorbed. The adsorbent layer 112 may include one buckypaper layeror a plurality of buckypaper layers, wherein each buckypaper layer mayhave a thickness in the range of 10-1,000 μm, preferably 100-900 μm,more preferably 200-500 μm. The plasma activated carbon nanotubes may besubstantially aligned or randomly oriented in the buckypaper.

Furthermore, the water treatment system may include a layer of sand,gravel, coarse silica, and/or ceramic particles to remove suspendedsolids and sediments. Said particles, i.e. sand, gravel, silica, orceramic particles, may have a hydrophilic coating, e.g. an acrylicpolymer such as poly(acrylic acid) or poly(acrylamide), poly(ethyleneglycol), poly(ethylene oxide), poly(vinyl alcohol), poly(vinylpyrrolidone). In one embodiment, said layer of sands, gravels, coarsesilica, and/or ceramic particles are secured in a cotton pad or a fabricand located inside the filter housing preferably between the adsorbentlayer 112 and the inlet 114. A second layer of sands, gravels, coarsesilica, and/or ceramic particles may also be located in the filterhousing and between the fibrous filter 110 and the outlet 116.

One aspect of the invention relates to a method of fabricating thefibrous filter 110. According to the method, a colloidal suspension ofsilver nanoparticles, polyvinylpyrrolidone (PVP), and dimethylformamide(DMF) is mixed with a ketone-based solvent to form a precursorsuspension. Exemplary ketone-based solvents include, but are not limitedto acetone, acetophenone, butanone, cyclopentanone, 2-pentanone,3-pentanone, isophorone, methyl isopropyl ketone, and ethyl isopropylketone. However, in a preferred embodiment, the ketone-based solvent isacetone, and the colloidal suspension is mixed with acetone at a volumeratio of 3:1 to 5:1, preferably 3.5:1 to 4.5:1, more preferably about4:1.

The polyvinylpyrrolidone present in the colloidal suspension may have aweight average molecular mass of 10,000-400,000 dalton, preferably50,000-350,000 dalton, preferably 100,000-300,000 dalton. Also, silvernanoparticles present in the colloidal suspension may be in the form ofa powder, or in a form of a suspension. A concentration ofpolyvinylpyrrolidone in the colloidal suspension is preferably no morethan 20 vol %, preferably no more than 25 vol %, relative to the totalvolume of the colloidal suspension. Also, an amount of silvernanoparticles in the colloidal suspension is preferably no more than 2wt %, preferably no more than 5 wt %, relative to the total weight ofthe colloidal suspension.

The method of fabricating the fibrous filter further involves mixingpolyvinylidene fluoride (PVDF) with the precursor suspension to form afirst suspension. The polyvinylidene fluoride as used herein may have aweight average molecular mass of 75,000-700,000 dalton, preferably100,000-650,000 dalton, preferably 200,000-600,000 dalton. Preferably,an amount of polyvinylidene fluoride in the first suspension is in therange of 10 to 20 wt %, preferably 12 to 18 wt %, preferably 15 to 17 wt%, preferably about 16 wt %, relative to the total weight of the firstsuspension. In a preferred embodiment, polyvinylidene fluoride is mixedwith the precursor suspension at a temperature in the range of 80 to100° C., preferably 85 to 95° C., preferably about 90° C.

Besides mixing the polyvinylidene fluoride with the precursorsuspension, polymethylmethacrylate is separately mixed with theprecursor suspension to form a second suspension. Thepolymethylmethacrylate as used herein may have a weight averagemolecular mass of 15,000-900,000 dalton, preferably 50,000-800,000dalton, preferably 100,000-750,000 dalton. Preferably, an amount ofpolymethylmethacrylate in the second suspension is in the range of 10 to20 wt %, preferably 12 to 18 wt %, preferably 15 to 17 wt %, preferablyabout 16 wt %, relative to the total weight of the second suspension. Ina preferred embodiment, polymethylmethacrylate is mixed with theprecursor suspension at a temperature in the range of 35 to 60° C.,preferably 40 to 50° C., preferably about 45° C.

The method of fabricating the fibrous filter further involves mixing thefirst suspension with the second suspension at a temperature in therange of 35 to 60° C., preferably 40 to 50° C., preferably about 45° C.,to form an electrospin suspension. Preferably, the first suspension ismixed with the second suspension at a volume ratio of 2:1 to 4:1,preferably 2.5:1 to 3.5:1, preferably about 3:1.

In a preferred embodiment, a carbon nanotube suspension that includescarbon nanotubes in dimethylformamide is mixed with the electrospinsuspension. The carbon nanotube suspension may preferably have a carbonnanotube concentration in the range of 0.5 to 2 g/L, preferably 0.7 to1.5 g/L, preferably about 1 g/L. The carbon nanotube suspension ispreferably mixed with the electrospin suspension at a volume ratio of1:6 to 1:10, preferably 1:7 to 1:9, preferably about 1:8. Theelectrospin suspension may be sonicated after mixing with the carbonnanotube suspension and before electrospinning. Accordingly, theelectrospin is sonicated for at least 30 minutes, preferably at least 1hour, but no more than 2 hours.

The electrospin suspension is further electrospun to form the fibrousfilter that includes polymer fibers of polymethylmethacrylate,polyvinylidene fluoride, and polyvinylpyrrolidone, and further includessilver nanoparticles that are deposited on the polymer fibers, andoptionally carbon nanotubes that are dispersed within the polymerfibers. The polymer fibers are shown in FIG. 3. The polymer fibers maybe hydrophobic, wherein a water contact angle of the polymer fibersranges from about 1200 to about 1300, preferably from about 124° toabout 126° (as shown in FIG. 5).

The electrospin suspension is electrospun with a syringe needle havingan outside diameter in the range of 0.15 to 1.5 mm, preferably 0.2 to1.25 mm; and an internal diameter in the range of 0.05 to 0.9 mm,preferably 0.08 to 0.85 mm. Electrospinning the electrospin suspensionis conducted, wherein a flow rate of the electrospin suspension thatcomes out of the syringe needle is in the range of 0.1 to 5 mL/h,preferably 0.2 to 4.8 mL/h, preferably 0.3 to 4.5 mL/h, and wherein avoltage in the range of 10 to 32 kV, preferably 12 to 30 kV is applied.

According to a second aspect, the present disclosure relates to a methodof forming purified water from a water stream, e.g. contaminated water,with the water treatment system.

The term “water” as used herein preferably refers to water having atotal organic carbon content of at least 4 ppm, or at least 5 ppm, or atleast 10 ppm, or at least 50 ppm, or at least 100 ppm, or at least 500ppm, or at least 1000 ppm. Alternatively, the term “water” may refer towastewater from various sources, ocean or sea water, river water, etc.In addition, the term “purified water” as used herein refers to waterhaving a total organic carbon content of less than 10 ppm, preferablyless than 5 ppm, preferably less than 4 ppm, preferably less than 3 ppm,preferably less than 2 ppm, preferably less than 1 ppm.

In one embodiment, the water treatment system consists of the pipe, thetransparent section, and the photocatalytic nanocomposite sheet.Accordingly, the adsorbent layer and the fibrous filter are not presentin this embodiment. In view of this embodiment water, i.e. contaminatedwater, is delivered to the water inlet 101 of the pipe from an upstreamsource, e.g. a wastewater tank 122, etc. Said contaminated water ispassed through the transparent section of the pipe, wherein a portion oforganic pollutants present in the contaminated water are decomposed, andrelatively purified water is obtained from a collector 106 that islocated downstream of the transparent section 102 and upstream of thefilter housing 108, and fluidly connected to the pipe 104.

In one embodiment, passing water, i.e. contaminated water, through thephotocatalytic nanocomposite sheet 105 reduces a total organic carboncontent present in said contaminated water by about 20% to about 30%,preferably about 24% to about 28% of a total organic carbon contentpresent in said contaminated water. For example, in one embodiment,passing contaminated water with a total organic carbon content of about10 to 10,000 ppm, preferably 50 to 9,000 ppm, preferably 100 to 8,000ppm, preferably 200 to 7,000 ppm, preferably 300 to 6,000 ppm,preferably 400 to 5,000 ppm, preferably 500 to 4,000 ppm, preferably 600to 3,000 ppm, preferably 700 to 2,000 ppm, preferably 800 to 1,000 ppm,through the photocatalytic nanocomposite sheet, may form purified waterhaving a total organic carbon content of about 8 to 8,000 ppm,preferably 40 to 7,000 ppm, preferably 80 to 7,000 ppm, preferably 150to 6,000 ppm, preferably 250 to 5,000 ppm, preferably 300 to 4,000 ppm,preferably 400 to 3,000 ppm, preferably 450 to 2,500 ppm, preferably 550to 1,800 ppm, preferably 600 to 800 ppm. In another embodiment, passingcontaminated water with a total organic carbon content of about 1 to 50ppm, preferably about 3 to 20 ppm, preferably about 4.5 to 5 ppm,preferably about 4.6 ppm, through the photocatalytic nanocompositesheet, may form purified water having a total organic carbon content ofabout 0.8 to 45 ppm, preferably about 2.5 to 15 ppm, preferably about3.3 to 3.5 ppm, preferably about 3.4 ppm.

The term “Total Organic Carbon (TOC)” as used herein refers to theamount of carbon found in water, e.g. contaminated water or purifiedwater, and may be used as an indicator of water quality or cleanlinessof the water sample.

In a preferred embodiment, the water treatment system further comprisesthe filter housing 108 that includes the adsorbent layer 112 and thefibrous filter 110, wherein the inlet 114 of the filter housing 108 isfluidly connected to the water outlet 107 of the pipe 104. Accordingly,the method of purifying involves passing the contaminated water throughboth the photocatalytic nanocomposite sheet, the adsorbent layer, andthe fibrous filter to form purified water. In view of this embodiment,the contaminated water is first delivered to the water inlet 101 of thepipe from an upstream source, e.g. a wastewater tank 122, etc. Saidcontaminated water is first passed through the transparent section ofthe pipe, wherein a portion of organic pollutants present in thecontaminated water is decomposed. Then, said contaminated water ispassed through the adsorbent layer and the fibrous filter present insidethe filter housing, wherein at least a portion of organic pollutantsthat may or may not have been decomposed in the photocatalyticnanocomposite sheet is adsorbed by the adsorbent layer and the fibrousfilter. In addition, solid particles that are suspended in water andhaving an average particle size of more than 50 nm, preferably more than40 nm, may also be filtered. Moreover, the contaminated water may bedisinfected due to the presence of the silver nanoparticles, and thusmicroorganisms and bacteria may be removed. As a result, purified wateris obtained from the outlet of the filter housing.

In one embodiment, passing contaminated water through the photocatalyticnanocomposite sheet, the adsorbent layer, and the fibrous filter causesa reduction of about 60% to about 75%, preferably about 65% to about 70%of a total organic carbon content present in the contaminated water.Accordingly, a ratio of a total organic carbon content of thecontaminated water to a total organic carbon content of the purifiedwater is in the range of 2:1 to 5:1, preferably 2.5:1 to 4:1, preferablyabout 3:1. For example, in one embodiment, passing contaminated waterwith a total organic carbon content of about 1 to 50 ppm, preferablyabout 3 to 20 ppm, preferably about 4.5 to 5 ppm, preferably about 4.6ppm, through the photocatalytic nanocomposite sheet, the adsorbentlayer, and the fibrous filter may form purified water having a totalorganic carbon content of about 0.3 to 20 ppm, preferably about 1 to 5ppm, preferably about 1.2 to 1.6 ppm, preferably about 1.5 ppm.

The phrase “passing contaminated water through a filter” as used hereinrefers to a process whereby the contaminated water from an upstreamsource, e.g. a wastewater tank 122, etc. is brought into contact withthe filter, and preferably a pressure is applied to force thecontaminated water through the filter (i.e. the photocatalyticnanocomposite sheet, the adsorbent layer, and the fibrous filter). Thepressure may be a positive pressure, which is provided by, for example,a positive displacement pump that is located upstream of and fluidlyconnected to the transparent section of the pipe (not shown).Alternatively, the pressure may be a negative pressure, which isprovided by, for example, a vacuum pump 118 that is located downstreamof and fluidly connected to the outlet 116 of the filter housing 108.Each of the positive or negative pressure may be in a range of 1 to 10bars, preferably 2 to 8 bars, preferably about 4 bars.

By applying the pressure (i.e. the positive pressure and/or the negativepressure), water permeates through the photocatalytic nanocompositesheet, the adsorbent layer, and the fibrous filter of the watertreatment system, and purified water is collected via the outlet of thefilter housing. In one embodiment, a valve is disposed on the outlet tocontrol a flow rate of the purified water. A flow rate of the purifiedwater depends on a water permeability of the photocatalyticnanocomposite sheet, the adsorbent layer, and the fibrous filter, andalso the positive pressure and/or the negative pressure applied towater. Preferably, the water treatment system may produce purified waterwith a flow rate in the range of 0.5 to 100 L/min, preferably 1 to 50L/min, more preferably 2 to 20 L/min.

In another preferred embodiment, at least a portion of purified water,which is received from the outlet of the filter housing, is recycled tothe water inlet of the pipe, so the purified water is passed through thephotocatalytic nanocomposite sheet, the adsorbent layer, and the fibrousfilter. Accordingly, the total organic carbon content is reduced by atleast 80%, preferably at least 90%, more preferably at least 95%,relative to the total organic carbon content that was initially presentin the contaminated water.

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. The described embodiments, together with further advantages,will be best understood by reference to the following detaileddescription taken in conjunction with the accompanying drawings.

The examples below are intended to further illustrate protocols for thewater treatment system, and the method of fabricating the photocatalyticnanocomposite sheet and the fibrous filter, and are not intended tolimit the scope of the claims.

Example 1—Synthesis of Ag₃PO₄/PMMA Nanocomposite Sheet

The materials used to fabricate to Ag₃PO₄/PMMA nanocomposite sheet areAg₃PO₄ nanoparticles in powder form, polymethylmethacrylate (PMMA)(molecular weight can range from 15000-900000 dalton) and a chloroformsolvent. The experiment was performed as follow; Ag₃PO₄ nanoparticles inthe powder form were first mixed with PMMA in a chloroform solvent. In atypical case, 2 g of PMMA were added to 100 ml of chloroform andmagnetically stirred at 50° C. until a colorless homogenous solution wasobtained. Afterwards, 100 mg of Ag₃PO₄ nanoparticles was added to PMMAsolution and sonicated for 2 h then magnetically stirred for another 2 hto get a clear homogenous yellow solution. The prepared solution wascasted in pre-cleaned glass petri dish, wherein the chloroform solventwas evaporated and the formed sheet of Ag₃PO₄/PMMA nanocomposite wascollected. A photocatalytic experiment was conducted by placing theAg₃PO₄/PMMA nanocomposite sheet under intensified/concentrated sunlight.Two mirrors were used to intensify the sunlight to the sheet.

Example 2—Synthesis of Nanofibers Made from PMMA/PVDF/Ag/CNTs

The materials used to fabricate nanofibers made from PMMA/PVDF/Ag/CNTsare polymethylmetacrylate (PMMA) (molecular weight ranges from15000-900000 dalton), polyvinylidene fluoride (PVDF) (molecular weightranges from 75000-700000 dalton), polyvinylpyrrolidone (PVP) (molecularweight ranges from 10000-400000 dalton), N,N-dimethylformamide (DMF),acetone, silver nitrate (AgNO₃), carbon nanotubes that were made fromfly ash (CNTs).

To prepare nanofiber composites made from PMMA/PVDF/PVP/Ag/CNTs, anelectrospin suspension is first made as follows. Solution A was acolloidal silver nanoparticles stabilized by PVP in DMF solvent.Solution B formed by mixing solution A with acetone. Solution C was madeby mixing solution A with solution B at a ratio of 4:1 by volume.Solution D was prepared by dissolving PVDF in solution C, wherein aconcentration of PVDF was 16% by weight. Solution D was heated up to 90°C. to completely dissolve the polymer and then the solution cooled.Solution E was prepared similar to solution D by dissolving PMMA insolution C, wherein a concentration of PMMA was 16% by weight. SolutionE heated only up to 45° C. Solution F was made by mixing solution D withsolution E at a ratio 3:1 by volume. To this solution CNTs was alsoadded to increase the mechanical property of the nanofibers. It wasadded in the form of a solution of CNTs in DMF at a concentration of 1mg/ml. The ratio of CNTs solution to solution F was 0.5:4 by volume.Then, solution F that contains CNTs was continuously stirred andsimultaneously sonicated for 0.5 h. The solution F was furtherelectrospun using an electrospinning system manufactured by NANONCompany, Japan with a syringe needle of 18 to 36 gauge. The flow ratewas set in the range of 0.3 to 4.5 mL/h, while the applied voltage wasset to a value in the range of 12 to 30 KV. Formation of the nanofiberswas confirmed by a scanning electron microscope. Different samples ofwaste water containing different organic pollutants were evaluated forthe degradation of such pollutants using the above mentioned system.

Example 3—Plasma Activation of CNTs

Carbon nanotubes were activated by oxygen plasma using the microwavechemical vapor deposition system. In this experiment appropriate amountof CNTs was kept in a ceramic crucible and placed inside the chamber ofthe system. Then the chamber was evacuated. Oxygen gas was purged at aflow rate of 75 sccm. When the system was stabilized the plasma wasgenerated at a power of 500 Watt. The plasma was continued for 30 min.Finally the system was switch down and the sample was collected and usedin the water treatment system.

The carbon nanotubes (CNTs) used in this study was obtained from fly ashbased on the methodology described by Salah et al. [Numan Salah, FormingCarbon Nanotubes from Carbon rich fly ash, U.S. Pat. No. 8,609,189 B2;Numan Salah, Sami S Habib, Zishan H Khan, Attieh A Al-ghamdi, AdnanMemic, Formation of carbon nanotubes from carbon rich fly ash: growthparameters and mechanism, Materials and Manufacturing Processes, 31,(2016) 146].

Example 4—Designing the Water Purification System

The designed system consists of two parts. The first part contains thephotocatalyst sheets of Ag₃PO₄/PMMA nanocomposite. These sheets wereinserted in a coil-shape cylindrical glass tube, and then a number ofthese cylinders were sequentially connected and placed on a table. Thetable containing these cylinders can be directly exposed to the sunlightfor photocatalytic reaction and organic pollutant degradation. Sunlightintensity was also enhanced by placing a plurality of mirrors to reflectsunlight to the table.

The second part contains the filter made of PMMA/PVDF/Ag/CNTnanocomposites. This filter was used to stop the dust particles andadsorb the residue of organic pollutants. The filter also used to removebacteria, viruses, or other microorganisms present in the pollutantwater. This filter was connected to a vacuum pump to accelerate thewater flow through the filter. Above the filter various amounts ofplasma activated CNTs were also used to adsorb organic pollutants.

Example 5—Evaluating the Purification Process Using the System

The tubes containing the photocatalyst sheets were exposed to sunlightwith an illuminance of 100,000 lux during fixed period of daylight.Direct and intensified/concentrated sunlight were reflected to the tablecontaining the photocatalyst sheets. The pollutant water (i.e. withmethylene blue at a concentration of 4 ppm) was flowed inside the glasstubes containing the sheets and after five minutes of exposure, a fewdrops of treated water were collected for analysis. Then, this treatedwater was passed to the second unit, which contains the plasma activatedCNTs and the filter membrane. Purified water was collected by the helpof a sucking system (e.g. a vacuum pump). Other organic pollutants werealso evaluated for the degradation/adsorption using this system. Thenthe collected samples were studied by UV-Vis absorption spectra for thedetermination of pollutant degradation. The collected samples after thefirst and second stage were also subjected to a HPLC analyzer (HPLC,SPD-20A, Shimadzu Corporation, Japan). A total organic carbon, TOCanalysis, (TOC-VCPH total carbon analyzer, Shimadzu Corporation, Japan)were also performed and the results are listed in Table 1. The resultsshow the TOC values in ppm of a distilled water sample, a water samplecontaminated with methylene blue, a water sample after treating saidcontaminated water with the photocatalyst sheets, and a water sampleafter treating said contaminated water with the plasma activated CNTsand the fibrous filter. The water sample after treating saidcontaminated water with the plasma activated CNTs and the fibrous filterhas a TOC value of less than 1 ppm, considering an initial TOC of purewater.

Two contaminated water samples, one containing methylene blue as thecontaminant and the other with Congo red as the contaminant, wereprepared and treated with the water treatment system. FIG. 6 shows eachof those samples before and after treatment using the water treatmentsystem.

FIG. 7 shows UV/Vis absorption spectra of contaminated water samples andthe curves show the absorption peak of methylene blue a) before anytreatment, b) after treatment with only the photocatalytic nanocompositesheet, c) after treatment with the photocatalytic nanocomposite sheetand the fibrous filter. The peak that corresponds to the presence ofmethylene blue disappeared after treatment with the photocatalyticnanocomposite sheet and the fibrous filter indicating a completedegradation of methylene blue.

FIG. 8 shows HPLC profiles of contaminated water samples havingmethylene blue, a) before any treatment, b) after treatment with onlythe photocatalytic nanocomposite sheet, c) after treatment with thephotocatalytic nanocomposite sheet and the fibrous filter. The peaksthat correspond to the presence of methylene blue disappear, whichindicates a complete degradation/removal of methylene blue aftertreatment.

TABLE 1 TOC removal (mineralization) of methylene blue using the newwater purification system. Sample TOC result (PPM) Pure water 0.81Un-treated waste water 4.60 Treated by photocatalyst 3.42 Final treatedby adsorption and filter 1.51

The invention claimed is:
 1. A water treatment system, comprising: apipe comprising a water inlet, a water outlet, and a transparent sectionlocated between the water inlet and the water outlet; and aphotocatalytic nanocomposite sheet comprising polymethylmethacrylate andsilver phosphate located inside the transparent section, wherein thephotocatalytic nanocomposite sheet is configured to decompose at least aportion of organic pollutants present in water.
 2. The water treatmentsystem of claim 1, wherein the transparent section is coil shaped. 3.The water treatment system of claim 1, wherein the photocatalyticnanocomposite sheet has a thickness in the range of 0.5 to 2 mm.
 4. Thewater treatment system of claim 1, further comprising: at least onemirror configured to reflect sunlight to the transparent section.
 5. Thewater treatment system of claim 1, further comprising: a filter housingwith an inlet and an outlet; and a fibrous filter located inside thefilter housing and between the inlet and the outlet, wherein the inletis fluidly connected to the water outlet.
 6. The filtration system ofclaim 5, wherein the fibrous filter comprises polymer fibers comprisingpolymethylmethacrylate, polyvinylidene fluoride, andpolyvinylpyrrolidone, and silver nanoparticles deposited on the polymerfibers.
 7. The water treatment system of claim 6, wherein the fibrousfilter has pores with an average pore size in the range of 5 to 50 nm.8. The water treatment system of claim 6, wherein the fibrous filterfurther comprises carbon nanotubes that are dispersed in the polymerfibers.
 9. The water treatment system of claim 5, further comprising: anadsorbent layer of plasma activated carbon nanotubes located in thefilter housing between the fibrous filter and the inlet.
 10. A method ofpurifying water with the water treatment system of claim 1, comprising:passing the water through the photocatalytic nanocomposite sheet to formpurified water.
 11. The method of claim 10, wherein the water treatmentsystem further comprises a filter housing with an inlet and an outlet,wherein the inlet is fluidly connected to the water outlet, and afibrous filter located inside the filter housing and between the inletand the outlet, the method comprising: passing the water through thephotocatalytic nanocomposite sheet and the fibrous filter to formpurified water.
 12. The method of claim 11, wherein a ratio of a totalorganic carbon content of the water to a total organic carbon content ofthe purified water is in the range of 2:1 to 5:1.